Technical Field
The disclosure concerns a plasma-enhanced reactive ion etch (PERIE) process for a workpiece such as a semiconductor wafer.
Background Discussion
In conventional atomic layer etching, a PERIE process removes an overlying layer {e.g., silicon dioxide) formed on a base layer (e.g., crystalline Silicon) of a workpiece, which may be a silicon wafer for example. The removal is performed one atomic layer at a time, as follows: The top atomic layer is passivated by a exposing the workpiece to a passivating process gas for the amount of time required for just one atomic layer to react with the passivating process gas, leaving underlying atomic layers unchanged. The one atomic layer that has been thus passivated may be referred to as the passivated layer. Species from the passivating process gas are chemically bound with material in the passivated layer, altering its characteristics. The passivated layer is susceptible to etching by a particular etch species, while the underlying layers remain relatively impervious to the particular etch species. The passivated layer is then etched by removing the passivating process gas and exposing the workpiece to a different process gas, namely an etching process gas containing the particular etch species. The foregoing processes of passivation and etching, including the changes of process gases, are then repeated for the next atomic layer. The cycle is continued until all atomic layers have been removed. One problem with this conventional process is that the RF bias voltage, typically of a sinusoidal type of waveform, produces a wide distribution of ion energies among the population of ions. Moreover, use of a capacitively or inductively coupled plasma source contributes to ion energy distribution and width of the ion energy distribution. A wide ion energy distribution leads to imprecise control over the thickness of material removed in each successive etching operation, so that the thickness may deviate from that of a single atomic layer.